This invention relates to a weft yarn gripping an element for gripping and transporting the weft yarn through the shed in continuous weft feed looms, of the type which is projected from one end of the shed to the other, and recovered from the latter.
Weft yarn gripping and transporting elements are already available in the form of an elongated flattened body of aerodynamic shape, comprising at its end means for gripping the yarn in the form of pincer arms normally in mutual engagement by the action of a spring, and disengageable by the action of a jack which causes them to diverge for feeding or freeing the weft yarn. The weft yarn fed to these elements of known type must be brought exactly into position between the pincer arms at the exact moment in which they open in order to become locked when they re-close, and this evidently requires weft yarn feed devices of considerable precision and corresponding high cost and constructional complication, and leads to a certain uncertainty in the working, since small differences in the operation of the various machine members, or slight deformation of the fed yarn, can easily produce the missing of picks in the loom, because of the weft yarn not being gripped by said members.
Weft yarn gripping and transporting elements are also available in the form of an elongated pincer grip divided at its front into two claws which strike the weft yarn during their travel so that it becomes inserted between the claws and is guided into engagement with elastic gripping means situated on one of the claws.
The gripping and transporting elements of this second type are evidently more reliable in that, while in the case of the former elements any traction force on the transported yarn can prejudice the grip, the yarn being able to escape from the pincer arms which grip it, in the case of the latter elements, the more the yarn is pulled, the more it becomes wedged in the gripping means, and its engagement is in fact of the self-locking type. Changes in the tension of the weft yarn, which are always possible during the travel of the transportation element, can therefore be dangerous in the first case but are perfectly absorbed in the second.
Moreover the gripping and transporting elements of the second type require weft yarn feed devices much simpler than those of the first type, in that they are apt to strike and retain (and then transport) even the weft yarn which is disposed on their path in a relatively approximate manner. However, because of their structure and far wider transverse dimensions, they are not suitable for application to those looms which use a plurality of gripping members projected into the shed in rapid succession. As it has not been possible up to the present time to adapt them to these latter looms, they have found application only in continuous weft feed looms in which the weft transportation elements are caused to make a simple to-and-fro movement, being driven by belts or rods subject to reciprocating motion.